The teichuronic acid of the cell wall of Micrococcus lysodeikticus is synthesized in vitro by a particulate enzyme fraction which utilizes uridine diphosphate N-acetylglucosamine (UDP-GlcNAc), UDP-N-acetylmannosaminuronic acid (UDP-ManNAcUA) and UDP-glucose (UDP-Glc). Several intermediates have been observed and are in the process of being characterized. The intermediates (in the sequence of their synthesis) are presumed to be: GlcNAc-carrier lipid, ManNAcUA-GlcNAc-carrier lipid, (ManNacUA)2,-GlcNAc-carrier lipid, Glc-(ManNAcUA)2-GlcNAc-carrier lipid, and ManNAcUA-Glc-(ManNAcUA)2-GlcNAc-carrier lipid. The carrier lipid is probably undecaprenol monophosphate. BIBLIOGRAPHIC REFERENCES: Rohr, T.E., Levy, G.N., Stark, N.J. and Anderson, J.S., Initial Reactions in the Biosynthesis of the Teichuronic Acid of Micrococcus lysodeikticus Cell Walls, J. Biol. Chem., 252, in press (1977). Stark, N.J., Levy, G.N., Rohr, T.E. and Anderson, J.S., Reactions of the Second Stage of Biosynthesis of the Teichuronic Acid of Micrococcus lysodeikticus Cell Walls, J. Biol. Chem., 252, in press (1977).